The present invention relates to linear actuators and particularly to linear actuators of the type having a housing and a linearly reciprocable member disposed therein and projecting therefrom.
Linear actuators of many different types are well known and widely used to convert the power generated by hydraulic or electric motors or the like into linear motion. One popular type of linear actuator utilizes a stationary longitudinal housing in which is disposed and from which extends a reciprocable member for linear reciprocal movement relative to the housing. Since the reciprocal movement of the reciprocable member into and out of the housing will normally create widely varying changes in the available internal volumetric capacity of the housing thereby producing recurring increases and decreases in the internal pressure in the housing, actuators of this type are usually provided with a venting arrangement in the housing to permit the admission into and expulsion from the housing of ambient air responsive to the aforesaid volumetric and pressure changes in the housing, whereby the internal housing pressure is maintained in equilibrium during operation of the actuator to avoid any inhibitory or other deleterious effects on the operational performance of the actuator which might be caused by such pressure changes. It will accordingly be understood that such a linear actuator thus functions in this respect essentially as an air pump producing an alternate inflow thereinto and outflow therefrom of ambient air.
In many of the conventional applications to which linear actuators are put, the ambient air often contains moisture and airborne debris which, if drawn into the housing thereof through a vent arrangement therein, will accumulate on and possibly corrode the internal housing surfaces over a period of time and will eventually deleteriously affect the performance of the actuator or possibly cause failure or malfunctioning thereof. For example, linear actuators have particular applicability in heliostats and other solar tracking devices but, because such devices necessarily must operate outdoors in varying climatic conditions, problems are encountered in utilizing linear actuators of the above-described type since the interior of the housing is exposed through the air entering the vent arrangement therein to moisture, dirt, and other debris and to extremes in temperature. Linear actuators embodied in devices of this type must generally be capable of withstanding such conditions over extended periods of time with little or no maintenance and, accordingly, actuators of the above-described type are generally considered unacceptable for use in such systems without some protective arrangement being provided to prevent the entrance of debris and excess moisture into the actuator through its venting system.
In contrast, the present invention provides a unique arrangement for shielding the venting system of linear actuators which is particularly adapted to totally prevent the entrance into the actuator housing of debris of any type and excess moisture without inhibiting the unrestricted operation of the actuator by enclosing the venting system with a bladder arrangement and confining therewithin a controlled predetermined volume of clean air free of excess moisture for equilibrium flow through the venting system into and out of the housing to maintain equilibrium pressure in the actuator housing during reciprocal operation of the actuator.